Genetic testing has transformed healthcare, guiding medical decisions, particularly in complex diseases like cancer. Somatic testing represents a significant advancement within genetic analysis, focusing on changes acquired during a person’s lifetime rather than those inherited. Its increasing role in personalized medicine offers tailored treatments and improved patient outcomes.
What is Somatic Testing?
Somatic testing analyzes genetic alterations that arise in specific cells after conception. These changes, called somatic mutations, are not present at birth and are not passed down to future generations. The testing identifies different types of genetic changes, such as point mutations, insertions, deletions, or larger chromosomal alterations. For example, it might detect an amplification (an increase in gene copies) or a specific gene mutation. These changes can disrupt normal cell functions, contributing to cancer development.
How Somatic Testing Differs from Germline Testing
Somatic and germline testing are distinct forms of genetic analysis. Germline testing investigates inherited genetic changes that are present in every cell of an individual’s body from birth. These inherited mutations can be passed down from parents to their children. In contrast, somatic testing focuses on acquired genetic changes found only in specific cells or tissues, such as tumor cells. These somatic mutations are not inherited and are typically isolated to the cancerous tissue. While germline testing aims to identify inherited cancer risks or carrier status for genetic conditions, somatic testing’s primary purpose is to characterize a tumor’s unique genetic profile to guide treatment decisions. For instance, a germline test might reveal a BRCA1 mutation indicating an inherited predisposition to breast cancer, whereas a somatic test would pinpoint a specific mutation within a patient’s tumor that could respond to a targeted therapy. Some laboratories offer paired somatic-germline testing, which analyzes both tumor and non-tumor samples to differentiate between acquired and inherited variants.
Applications in Cancer Treatment
Somatic testing provides information about a tumor’s genetic makeup. It helps identify specific genetic alterations, or “driver mutations,” that contribute to cancer growth and can be targeted by particular therapies. For example, identifying mutations in genes like EGFR or BRAF can guide the use of targeted drugs designed to block their activity. This testing helps predict how a patient’s cancer might respond to treatments, including targeted therapies and immunotherapies. For instance, the presence of homologous recombination deficiency (HRD) or microsatellite instability (MSI) can indicate a potential response to specific drugs like PARP inhibitors or checkpoint inhibitors. Somatic testing can also be used to monitor disease progression by detecting changes in tumor DNA over time and identify mechanisms of drug resistance, allowing clinicians to adjust treatment plans. This information contributes to personalized treatment strategies.
The Somatic Testing Process
The somatic testing process typically begins with obtaining a sample from the patient. This often involves a tissue biopsy, where a small piece of the tumor is surgically removed. Alternatively, a liquid biopsy may be used, which involves collecting a blood sample to detect circulating tumor DNA (ctDNA) released by cancer cells into the bloodstream. Liquid biopsies offer a less invasive option and can be especially useful when a tissue biopsy is difficult to obtain.
Once the sample is collected, DNA is extracted from the cells. This DNA then undergoes analytical methods to identify genetic changes. Next-generation sequencing (NGS) is a common technique, allowing for the simultaneous analysis of many genes or even the entire tumor genome. Other methods, like polymerase chain reaction (PCR), might be used for targeted analysis of specific mutations. The turnaround time for results can vary, but typically ranges from several days to a few weeks, depending on the complexity of the test and the laboratory.
Understanding Somatic Test Results
Somatic test results provide a detailed report of the genetic alterations found within the tumor cells. This report often highlights specific mutations or amplifications and includes information about their clinical significance. For instance, it might indicate whether a particular mutation is associated with sensitivity or resistance to certain cancer therapies.
These results are then interpreted by a medical team, usually including an oncologist and sometimes a genetic counselor. The team uses this information to develop a personalized treatment plan, considering the patient’s specific cancer type and the identified genetic alterations. The concept of “actionable” mutations is central to this interpretation; these are genetic changes that have known targeted therapies or clinical implications. While somatic testing focuses on tumor characteristics, a finding on a somatic test might occasionally suggest an underlying inherited predisposition, which could prompt further germline testing.